Detective Chief Inspector Phil Jones, who is leading the murder investigation, said: "I'm sure someone out there has that vital piece of information we need to catch Jo's killer. I would again urge anyone with any information whatsoever to come forward and help us find the answers that both ourselves and Jo's family want and need."

Meanwhile, the parents of a teenager from Yate, near Bristol, who was murdered in 1995 have urged police to DNA test people living close to Yeates's home.

Louise Smith, 18, was raped and killed as she walked home from a nightclub on Christmas Day. Avon and Somerset police took DNA samples from 5,000 men in the area when initial inquiries failed to trace the killer.

David Frost, a 21-year-old student, was caught 14 months after the murder when police noticed he had evaded giving a DNA sample.

Louise's mother, Gillian Smith, said: "They should test residents near where she lived in Clifton and where her body was found. The tension in Bristol and around Clifton will not be relieved until someone is caught."

A report has emerged that two "agitated" men were seen early today emerging from woodland near where Yeates's body was found.

The daughter of a motorist who spotted the suspicious activity reported the sighting on Facebook. She wrote: "My mum was driving past Longwood Lane on the way to work this morning at 6.20am and two men came out the woods [with] no coats on and soaking wet.

"They looked really agitated – one ran to the other side of the road. She thought they were going to jump in front of her car. She rang the police to let them know. What were they doing in the dark at that time of the morning?"

Avon and Somerset police refused to comment on the sighting.

Police have again attempted to dampen down expectation that the crime will be solved quickly, although Chief Superintendent Jon Stratford of Avon and Somerset police said steady progress was being made. "It could take some time before we find out who killed Jo but we certainly will," he said.

Stratford, who has responsibility for community policing in the Clifton area of Bristol where Yeates went missing, said a large police presence remained in the area to reassure people. Officers were making extra patrols on foot, in vehicles, on bicycles and on horseback.

Women have been advised not to walk home alone after dark but Stratford repeated that there was no specific intelligence to suggest an increased risk.

Yeates's landlord, Chris Jefferies, who was arrested on suspicion of her murder before being freed on police bail, may be thinking about legal action over his arrest, according to a friend.

Irving Steggles, 65, who works at a Baptist church in South Africa, said: "Chris emailed me and said he was going to be eliminated from police inquiries in the next day or so. He said: 'The ordeal is almost over.' He is preparing a case against the media and the police, I believe. This has completely shattered his life."